Falls, fall-related injury, and fear of falling affect functional mobility, independence, and quality of life in older Veterans. To date, little is known about the biomechanics and neuromuscular requirements of turning while walking tasks in older adults, even though falls during turning are 7.9 times more likely to lead to serious injury such as hip fracture than falls during straight-line walking. This proposed pilot study will employ both experimental and computer simulation approaches to a) identify differences in turn mechanics between older adult fallers and non-fallers and b) determine if a previously validated musculoskeletal model for walking can be used to simulate turning while walking tasks. Twenty older adult fallers (age 65-80 years, at least two falls in the previous year, balance/gait impairment, lower extremity muscle weakness, and do not walk for exercise) and twenty age- and gender-matched non-fallers will be recruited from clinics at the VA GLAHS. Subjects will perform three successful trials of straight line walking, 900 and 1800 turns at their self-selected walking speed. Kinematics, ground reaction force, and muscle activity will be recorded synchronously. Total body center of mass trajectory, head, trunk, and lower extremity kinematics, ground reaction forces, lower extremity net joint moments and muscle activation patterns will be analyzed. Results will be averaged across three successful trials of each task and be compared between groups and tasks using a repeated measure ANOVA. The experimental results will be used to create and validate a three-dimensional musculoskeletal model that simulates turning tasks performed by older adults. The model will be based on one that was previously validated for straight-line gait by Fregly et al. We hypothesize that the new model will require increases in the degrees of freedom at the ankle and/or knee sufficient to simulate turning while walking tasks performed by older adults. Identification of between-group differences in turn mechanics will provide us with the baseline objective biomechanical and neuromuscular markers that can be used directly to develop evaluation and rehabilitation guidelines to improve turn performance in older Veterans. The experimentally validated musculoskeletal model created in this study will be used in our future research to investigate hypotheses that cannot be tested experimentally, such as the effect of systematically increasing muscle torque at a joint or modifying the timing and magnitude of muscle contractions on turn mechanics. The outcome of this work will provide the experimental results and simulation tools necessary for the next steps in improving our understanding of turn mechanics and identifying potential rehabilitation options specific to turning in older Veterans.